Distribution of inspiratory and expiratory respiratory sound intensity on the surface of the human thorax

Respiratory sounds were recorded simultaneously with 16 microphones distributed over the thoracic surface of 4 healthy subjects and one patient with lung consolidation. Acoustic energy in three frequency bands, 150-300 Hz, 300-600 Hz and 600-1200 Hz, was analyzed during inspiration and expiration at flow rates of 30 ml/s/kg. Our results indicate that on average, inspiratory sounds are 10 to 11 dB louder than expiratory sounds at comparable flow rates. The acoustic shadow produced by the heart is more pronounced during inspiration. These findings support the concept that inspiratory sounds are produced predominantly in the periphery of the lung, while expiratory sounds are generated more centrally. Furthermore, lung sounds were found to be significantly louder on the right side for the front part of the thorax, and on the left side for the back. In the patient with pneumonia and consolidation, lung sounds mainly above 300 Hz were less attenuated over the consolidated parts of the lung